Tin alloys



Patented Nov. 2, 1937 Es. PATENT OFFlCE 'rm ALLoYs m Daniel Haas, Haselor, Alcester, and William Thomas Pell-Walpole, Tipton, England, assignors to John Campbell, Kensington, England No Drawing.

Application November 28, 1936,

Serial No. 113,256. In Great Britain December 4 Claims.

This invention relates to tin alloys and methods of producing the same.

It is known that the metal tin, although ductile, is very Weak, and numerous metals have been 5 alloyed with tin. with the object of increasing its strength without seriously impairing its ductility. Thus, lead, bismuth and antimony are commonly used for this purpose and ductile alloys of tin with these and other metals: are largely used in making pewter and for the manufacture of tin foil, sheet and strip used for a variety of purposes such as the wrapping of goods, the making of collapsible metal containers, the construction of chemically resistant plant and vessels, and

the like. Such tin alloys, however, have suffered from the disadvantage that their strength could not be permanently improved by cold working or heat treatment since any advantage resulting from those processes was temporary in character and disappeared in the course of a few days or weeks at ordinary atmospheric temperatures.

The object of the present invention is to produce improved tin alloys having all the advantages of the known alloys but possessing also to an unusually high degree the capacity for withstanding stresses for very long periods at room temperatures. e

The invention consists in tin alloys containing from 2 to 14 per cent. of antimony and about 1 to 10 per cent. of the balance being tin.

The invention also consists in tin alloys according tothe preceding paragraph subjected to one or more predetermined heat treatments.

Further features of the invention will be apparent from the description given hereafter.

In carrying our invention into eifect in one convenient manner we may form our improved tin alloy according to any composition within the range 2 to 14 per cent. antimony and 1 to 10 per cent. cadmium, the balance being tin. Such alloys: are strong and in particular their mechanical properties may be modified and improved by heat treatment, the alloys being capable of being used in the cast or worked state.

When applying the improving heat treatment the alloys are first annealed within the temperature range 140 to 175 C. after which they may be cooled slowly as in a furnace, or rapidly by cooling in air, or in some liquid such as cold water or by any other known method of quenching. Some improvement is shewn in quite short periods (say, 15 minutes or even less) of such a heat treatment but the time necessary to give the maximum improvement in properties varies with the previous history of the alloy and can readily be determined by a few trials. After such treatment the alloys will be found to be stronger and to retain their improved properties permanently at ordinary temperatures. Still further improvements can be eifected by further annealing at a temperature which lies above 180 C. but below the temperature at which the particular alloy being treated begins to melt. The time during which any alloy is subjected to such heat treatment again varies with the previous history of the alloy and is usually not more than one hour but the appropriate time can be readily determined by a few trials. After this further annealing the alloys should preferably be cooled quickly as in air or in liquid although the rate of cooling may vary within comparatively wide limits without entirely altering the general eifect of the heat treatment.

When the second heat treatment is to be applied to an alloy the first heat treatment should be applied for a period sufiicient 'to remove all traces of the tin-cadmitun eutectic from the microstructure of the alloy, the appropriate time being readily ascertainable by examining the microstructure at intervals during the heat treatment.

It is found that all alloys within the specified range of composition are made stronger by the application of both forms of treatment as compared with their strength after the application of the first heat treatment only and that the improvement due to the second heat treatment is permanent and alters only slightly or not at all with time provided the alloys are used at atmospheric temperature.

Some of the alloys within the range given may be subjected to a third heat treatment consisting in heating to a temperature not exceeding C. If desired, the first two forms of heat treatment may be combined, in which case the alloys should be first heated for the appropriate time within the temperature range to C. and the temperature may thereafter be raised to between C. and the temperature at which the particular alloy under treatment begins to melt, the intermediate quenching or cooling process in such case being omitted.

. The actual percentage of the ingredients emthe alloy is to be used or any practical requirements that may have to be fulfilled.

We claim:

1. Tin alloys containing from 2 to 14 per cent. of antimony and about 1 to 10 per cent. of cadmium, the balance being tin.

2. Tin alloys according to claim 1 heat treated by annealing Within the range 140 C. to 175 C. and subsequent cooling.

3. Tin alloys according to claim 1 first heat treated by annealing within the range 140 C. to 175 C. and subsequent cooling, and thensubjected to a further heat treatment consisting of ing then rapidly cooled.

DANIEL HANSON.

WILLIAM THOMAS PELL-WALPOLE. 

